Can steam be usable as a “plus” for ventilation shutdown?

Abstract

SUMMARY: The American Veterinary Medical Association (AVMA), preferred depopulation methods (i.e., foam, containerized gassing, and mechanical methods) can be challenging when depopulating cage and aviary commercial laying hen houses for multiple reasons. When preferred methods are not feasible or resources are unavailable, ventilation shutdown plus (VSD+) heat and/or carbon dioxide (CO2) is approved for emergency situations. Both recognized “pluses” work but can have issues as VSD+ heat typically causes a decrease in environmental humidity and can affect PVC structures, while CO2 can be a human safety concern and has procurement problem during emergencies. Steam supplies both heat and humidity, the latter hindering birds’ ability to dissipate body heat through evaporative cooling, thus expediting hyperthermia. The objective of this study was to evaluate effectiveness of VSD+ with steam as a “plus” for depopulation of laying hens in a cage-free aviary system. Approximately 1,800 Lohmann Brown hens aged 56 wk were housed in Big Dutchman Natura 60 aviaries in 4 rooms. Four VSD+ treatments were as follows: 1) control or VSD+ heat (VSD-H), 2) VSD with steam (VSD-S), 3) VSD with heat and then steam to maintain temperature and humidity (VSD-HS), and 4) VSD with steam and then heat to maintain temperature (VSD-SH). All VSD+ procedures followed AVMA depopulation guidelines for temperature and time (i.e., 40°C within 30 min). Hens were monitored via cameras for times to first and 100% mortality. After depopulation was completed mortality location within each tier of system (floor area, first tier, second tier, and third tier) were recorded. Data were analyzed in SPSS v. 28 and significance was at P < 0.05. Observed time to first mortality for VSD-H, VSD-S, VSD-HS, and VSD-SH were 82.7-min, 56.6-min, 49.6-min, and 52-min. While 100% mortality for VSD-S was 112.3-min; VSD-HS was 83.3-min; VSD-SH was 103.6-min; and VSD-H never reached 100% mortality in time limit. Mortality location revealed VSD-S and VSD-SH had more carcasses located in floor area than VSD-HS (P = 0.02); VSD-S and VSD-SH had less carcasses than VSD-HS (P = 0.02) in first tier and third tier; no differences were observed between treatments in second tier (P = 0.248). Hens in steam treatments were faster in reaching time to first and 100% mortality than hens in VSD-H (P < 0.05). Results indicated that steam alone, or in combination with forced air heat, could be recognized and used as a “plus” for VSD+ depopulation of laying hens reared in a cage-free or aviary housing system.

Keywords

• laying hen
• mass depopulation
• VSD+
• steam